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https://www.readbyqxmd.com/read/29731952/the-strong-%C3%AE-cf-3-shielding-effect-in-hexafluoroisopropanol-and-100-other-organic-solvents-revisited-with-17-o-nmr-spectroscopy
#1
Annika Bernhardt, Harald Kelm, Frederic W Patureau
An 17 O NMR spectroscopy survey of more than 100 ubiquitous organic solvents and compounds, including some typical oxofluorinated solvents such as hexafluoroisopropanol, trifluoroethanol, trifluoroacetic acid, and others, is presented with D2 O as a reference. A strong alternating α,β-CF3 -substituent chemical shift effect was thus observed. This alternating deshielding-shielding effect is suspected to have a role in the exceptional properties of these oxofluorinated solvents, notably in oxidative cross-coupling reactions...
April 9, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29610628/selective-catalytic-oxidation-of-cyclohexene-with-molecular-oxygen-radical-versus-nonradical-pathways
#2
Ilse M Denekamp, Martijn Antens, Thierry K Slot, Gadi Rothenberg
We study the allylic oxidation of cyclohexene with O2 under mild conditions in the presence of transition-metal catalysts. The catalysts comprise nanometric metal oxide particles supported on porous N-doped carbons (M/N:C, M=V, Cr, Fe, Co, Ni, Cu, Nb, Mo, W). Most of these metal oxides give only moderate conversions, and the majority of the products are over-oxidation products. Co/N:C and Cu/N:C, however, give 70-80 % conversion and 40-50 % selectivity to the ketone product, cyclohexene-2-one. Control experiments in which we used free-radical scavengers show that the oxidation follows the expected free-radical pathway in almost all cases...
March 7, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29610627/colloidal-au-catalyst-preparation-selective-removal-of-polyvinylpyrrolidone-from-active-au-sites
#3
Baira Donoeva, Petra E de Jongh
Colloids with controlled dimensions, morphology and composition can be used to obtain supported metal catalysts with desired characteristics. Yet, removal of capping agents which block active metal sites in such catalysts can be challenging: mild methods often result in incomplete removal of capping agents, whereas harsher methods can cause change in particle size or morphology or cause metal segregation for bimetallic particles. Here we provide evidence that polyvinylpyrrolidone used as a stabilizing agent for gold colloids is present both on the metal and the support surface after colloid deposition on the TiO2 support...
March 7, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29541255/hydrogenation-of-lactic-acid-to-1-2-propanediol-over-ru-based-catalysts
#4
Kaituo Liu, Xiaoming Huang, Evgeny A Pidko, Emiel J M Hensen
The catalytic hydrogenation of lactic acid to 1,2-propanediol with supported Ru catalysts in water was investigated. The influence of catalyst support (activated carbon, γ-Al2 O3 , SiO2 , TiO2 , and CeO2 ) and promoters (Pd, Au, Mo, Re, Sn) on the catalytic performance was evaluated. Catalytic tests revealed that TiO2 yields the best Ru catalysts. With a monometallic Ru/TiO2 catalyst, a 1,2-propanediol yield of 70 % at 79 % lactic acid conversion was achieved at 130 °C after 20 h reaction. Minor byproducts of the hydrogenation reaction were propionic acid, ethanol, 1-propanol, and 2-propanol...
February 21, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29541254/exceptionally-efficient-and-recyclable-heterogeneous-metal-organic-framework-catalyst-for-glucose-isomerization-in-water
#5
Ryan Oozeerally, David L Burnett, Thomas W Chamberlain, Richard I Walton, Volkan Degirmenci
Heterogeneous catalysts are desired for the conversion of glucose, the most abundant sugar in renewable biomass, but presently their synthesis requires highly toxic chemicals with long synthesis times. We report the conversion of glucose into fructose and 5-hydroxymethylfurfural on a heterogeneous catalyst that is stable and selective and operates in the most environmentally benign solvent, water. We used a bifunctional solid with Lewis and Brønsted acid sites by partially replacing the organic linker of the zirconium organic framework UiO-66 with 2-monosulfo-benzene-1,4-dicarboxylate...
February 21, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29515675/hydrogen-borrowing-alcohol-bioamination-with-coimmobilized-dehydrogenases
#6
Wesley Böhmer, Tanja Knaus, Francesco G Mutti
The amination of alcohols is an important transformation in chemistry. The redox-neutral (i.e., hydrogen-borrowing) asymmetric amination of alcohols is enabled by the combination of an alcohol dehydrogenase (ADH) with an amine dehydrogenase (AmDH). In this work, we enhanced the efficiency of hydrogen-borrowing biocatalytic amination by co-immobilizing both dehydrogenases on controlled porosity glass FeIII ion-affinity beads. The recyclability of the dual-enzyme system was demonstrated (5 cycles) with total turnover numbers of >4000 and >1000 for ADH and AmDH, respectively...
February 2018: ChemCatChem
https://www.readbyqxmd.com/read/29399208/facile-synthesis-of-a-novel-hierarchical-zsm-5-zeolite-a-stable-acid-catalyst-for-dehydrating-glycerol-to-acrolein
#7
Rolf Beerthuis, Liang Huang, N Raveendran Shiju, Gadi Rothenberg, Wei Shen, Hualong Xu
Catalytic biomass conversion is often hindered by coking. Carbon compounds cover active surface and plug pores, causing catalyst deactivation. Material design at the nanoscale allows tailoring of the catalytic activity and stability. Here, we report a simple synthesis of nanosized ZSM-5 materials by using a silicalite-1 seeding suspension. ZSM-5 crystals were grown from a deionized silica source in the presence of ammonia. By using silicalite-1 seeds, crystalline ZSM-5 is synthesized without any structure-directing agent...
January 9, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29399207/mechanism-of-carbon-monoxide-dissociation-on-a-cobalt-fischer-tropsch-catalyst
#8
Wei Chen, Bart Zijlstra, Ivo A W Filot, Robert Pestman, Emiel J M Hensen
The way in which the triple bond in CO dissociates, a key reaction step in the Fischer-Tropsch (FT) reaction, is a subject of intense debate. Direct CO dissociation on a Co catalyst was probed by 12 C16 O/13 C18 O scrambling in the absence and presence of H2 . The initial scrambling rate without H2 was significantly higher than the rate of CO consumption under CO hydrogenation conditions, which indicated that the surface contained sites sufficiently reactive to dissociate CO without the assistance of H atoms...
January 9, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29242719/plasma-assisted-synthesis-of-monodispersed-and-robust-ruthenium-ultrafine-nanocatalysts-for-organosilane-oxidation-and-oxygen-evolution-reactions
#9
Edwin S Gnanakumar, Wesley Ng, Bilge Coşkuner Filiz, Gadi Rothenberg, Sheng Wang, Hualong Xu, Laura Pastor-Pérez, M Mercedes Pastor-Blas, Antonio Sepúlveda-Escribano, Ning Yan, N Raveendran Shiju
We report a facile and general approach for preparing ultrafine ruthenium nanocatalysts by using a plasma-assisted synthesis at <100 °C. The resulting Ru nanoparticles are monodispersed (typical size 2 nm) and remain that way upon loading onto carbon and TiO2 supports. This gives robust catalysts with excellent activities in both organosilane oxidation and the oxygen evolution reaction.
November 23, 2017: ChemCatChem
https://www.readbyqxmd.com/read/29503672/pd-catalyzed-versus-uncatalyzed-phi-oac-2-mediated-cyclization-reactions-of-n-6-1-1-biaryl-2-yl-adenine-nucleosides
#10
Sakilam Satishkumar, Suresh Poudapally, Prasanna K Vuram, Venkateshwarlu Gurram, Narender Pottabathini, Dellamol Sebastian, Lijia Yang, Padmanava Pradhan, Mahesh K Lakshman
In this work we have assessed reactions of N 6 -([1,1'-biaryl]-2-yl)adenine nucleosides with Pd(OAc)2 and PhI(OAc)2 , via a PdII /PdIV redox cycle. The substrates are readily obtained by Pd/Xantphos-catalyzed reaction of adenine nucleosides with 2-bromo-1,1'-biaryls. In PhMe, the N 6 -biarylyl nucleosides gave C6-carbazolyl nucleoside analogues by C-N bond formation with the exocyclic N 6 nitrogen atom. In the solvent screening for the Pd-catalyzed reactions, an uncatalyzed process was found to be operational...
November 9, 2017: ChemCatChem
https://www.readbyqxmd.com/read/29201243/on-the-role-of-acidity-in-bulk-and-nanosheet-t-mfi-t-al-3-ga-3-fe-3-b-3-zeolites-in-the-methanol-to-hydrocarbons-reaction
#11
Lingqian Meng, Xiaochun Zhu, Brahim Mezari, Robert Pestman, Wannaruedee Wannapakdee, Emiel J M Hensen
The influence of framework substituents (Al3+ , Ga3+ , Fe3+ and B3+ ) and morphology (bulk vs. nanometer-sized sheets) of MFI zeolites on the acidity and catalytic performance in the methanol-to-hydrocarbons (MTH) reaction was investigated. The Brønsted acid density and strength decreased in the order Al(OH)Si>Ga(OH)Si>Fe(OH)Si≫B(OH)Si. Pyridine15 N NMR spectra confirmed the differences in the Brønsted and Lewis acid strengths but also provided evidence for site heterogeneity in the Brønsted acid sites...
October 23, 2017: ChemCatChem
https://www.readbyqxmd.com/read/29201242/selective-photooxidation-reactions-using-water-soluble-anthraquinone-photocatalysts
#12
Wuyuan Zhang, Jenő Gacs, Isabel W C E Arends, Frank Hollmann
The aerobic organocatalytic oxidation of alcohols was achieved by using water-soluble sodium anthraquinone sulfonate. Under visible-light activation, this catalyst mediated the aerobic oxidation of alcohols to aldehydes and ketones. The photo-oxyfunctionalization of alkanes was also possible under these conditions.
October 23, 2017: ChemCatChem
https://www.readbyqxmd.com/read/29399209/automated-determination-of-oxygen-dependent-enzyme-kinetics-in-a-tube-in-tube-flow-reactor
#13
Rolf H Ringborg, Asbjørn Toftgaard Pedersen, John M Woodley
Enzyme-mediated oxidation is of particular interest to synthetic organic chemists. However, the implementation of such systems demands knowledge of enzyme kinetics. Conventionally collecting kinetic data for biocatalytic oxidations is fraught with difficulties such as low oxygen solubility in water and limited oxygen supply. Here, we present a novel method for the collection of such kinetic data using a pressurized tube-in-tube reactor, operated in the low-dispersed flow regime to generate time-series data, with minimal material consumption...
September 8, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28736581/the-remarkable-amphoteric-nature-of-defective-uio-66-in-catalytic-reactions
#14
Julianna Hajek, Bart Bueken, Michel Waroquier, Dirk De Vos, Veronique Van Speybroeck
One of the major requirements in solid acid and base catalyzed reactions is that the reactants, intermediates or activated complexes cooperate with several functions of catalyst support. In this work the remarkable bifunctional behavior of the defective UiO-66(Zr) metal organic framework is shown for acid-base pair catalysis. The active site relies on the presence of coordinatively unsaturated zirconium sites, which may be tuned by removing framework linkers and by removal of water from the inorganic bricks using a dehydration treatment...
June 22, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28670348/proton-reduction-reaction-catalyzed-by-homoleptic-nickel-bis-1-2-dithiolate-complexes-experimental-and-theoretical-mechanistic-investigations
#15
Athanasios Zarkadoulas, Martin J Field, Vincent Artero, Christiana A Mitsopoulou
A series of homoleptic monoanionic nickel dithiolene complexes [Ni(bdt)2](NBu4), [Ni(tdt)2](NBu4), and [Ni(mnt)2](NBu4) containing the ligands benzene-1,2-dithiolate (bdt2-), toluene-3,4-dithiolate (tdt2-) and maleonitriledithiolate (mnt2-), respectively, have been employed as electrocatalysts in the hydrogen evolution reaction with trifluoroacetic acid as proton source in acetonitrile. All complexes were active catalysts with TONs reaching 113, 158 and 6 for [Ni(bdt)2](NBu4), [Ni(tdt)2](NBu4), and [Ni(mnt)2](NBu4), respectively...
June 22, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28919932/separating-thermodynamics-from-kinetics-a-new-understanding-of-the-transketolase-reaction
#16
Stefan R Marsden, Lorina Gjonaj, Stephen J Eustace, Ulf Hanefeld
Transketolase catalyzes asymmetric C-C bond formation of two highly polar compounds. Over the last 30 years, the reaction has unanimously been described in literature as irreversible because of the concomitant release of CO2 if using lithium hydroxypyruvate (LiHPA) as a substrate. Following the reaction over a longer period of time however, we have now found it to be initially kinetically controlled. Contrary to previous suggestions, for the non-natural conversion of synthetically more interesting apolar substrates, the complete change of active-site polarity is therefore not necessary...
May 23, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28706570/the-effects-of-secondary-oxides-on-copper-based-catalysts-for-green-methanol-synthesis
#17
James S Hayward, Paul J Smith, Simon A Kondrat, Michael Bowker, Graham J Hutchings
Catalysts for methanol synthesis from CO2 and H2 have been produced by two main methods: co-precipitation and supercritical anti-solvent (SAS) precipitation. These two methods are compared, along with the behaviour of copper supported on Zn, Mg, Mn, and Ce oxides. Although the SAS method produces initially active material with high Cu specific surface area, they appear to be unstable during reaction losing significant amounts of surface area and hence activity. The CuZn catalysts prepared by co-precipitation, however, showed much greater thermal and reactive stability than the other materials...
May 10, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28706569/supercritical-antisolvent-precipitation-of-amorphous-copper-zinc-georgeite-and-acetate-precursors-for-the-preparation-of-ambient-pressure-water-gas-shift-copper-zinc-oxide-catalysts
#18
Paul J Smith, Simon A Kondrat, James H Carter, Philip A Chater, Jonathan K Bartley, Stuart H Taylor, Michael S Spencer, Graham J Hutchings
A series of copper-zinc acetate and zincian georgeite precursors have been produced by supercritical CO2 antisolvent (SAS) precipitation as precursors to Cu/ZnO catalysts for the water gas shift (WGS) reaction. The amorphous materials were prepared by varying the water/ethanol volumetric ratio in the initial metal acetate solutions. Water addition promoted georgeite formation at the expense of mixed metal acetates, which are formed in the absence of the water co-solvent. Optimum SAS precipitation occurs without water to give high surface areas, whereas high water content gives inferior surface areas and copper-zinc segregation...
May 10, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28580035/acetic-acid-ketonization-over-fe3o4-sio2-for-pyrolysis-bio-oil-upgrading
#19
James A Bennett, Christopher M A Parlett, Mark A Isaacs, Lee J Durndell, Luca Olivi, Adam F Lee, Karen Wilson
A family of silica-supported, magnetite nanoparticle catalysts was synthesised and investigated for continuous-flow acetic acid ketonisation as a model pyrolysis bio-oil upgrading reaction. The physico-chemical properties of Fe3O4/SiO2 catalysts were characterised by using high-resolution transmission electron microscopy, X-ray absorption spectroscopy, X-ray photo-electron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, thermogravimetric analysis and porosimetry. The acid site densities were inversely proportional to the Fe3O4 particle size, although the acid strength and Lewis character were size-invariant, and correlated with the specific activity for the vapour-phase acetic ketonisation to acetone...
May 10, 2017: ChemCatChem
https://www.readbyqxmd.com/read/28529668/diastereoselective-radical-type-cyclopropanation-of-electron-deficient-alkenes-mediated-by-the-highly-active-cobalt-ii-tetramethyltetraaza-14-annulene-catalyst
#20
Andrei Chirila, Braja Gopal Das, Nanda D Paul, Bas de Bruin
A new protocol for the catalytic synthesis of cyclopropanes using electron-deficient alkenes is presented, which is catalysed by a series of affordable, easy to synthesise and highly active substituted cobalt(II) tetraaza[14]annulenes. These catalysts are compatible with the use of sodium tosylhydrazone salts as precursors to diazo compounds in one-pot catalytic transformations to afford the desired cyclopropanes in almost quantitative yields. The reaction takes advantage of the metalloradical character of the Co complexes to activate the diazo compounds...
April 21, 2017: ChemCatChem
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